Automatic analyzers analyze the constituents of a substance such as blood and urine. Such an automatic analyzer includes a reaction cell that holds a reaction solution prepared by causing a reaction between a sample and a reagent, a sample dispensing probe that dispenses a predetermined amount of the reagent into the reaction cell from a sample container holding the sample, and a reagent dispensing probe that dispenses a predetermined amount of the reagent into the reaction cell from a reagent container holding the reagent. The analyzer causes the chemical reaction between the liquid sample and reagent dispensed from the sample dispensing probe and the reagent dispensing probe into the reaction cell, irradiating the resulting reaction solution with light from a halogen lamp or the like, measuring absorbance of the solution, and thus analyzing a constituent of the liquid sample.
In recent years, reduction in running costs of automatic analyzers by saving reagent consumption has been demanded. To meet this demand, the amount of sample dispensed is preferably decreased to lessen the amount of a reaction solution, while maintaining a ratio between the amount of sample and that of reagent. Accuracy in a trace amount of dispensing, therefore, is now an important factor in ensuring data reliability.
The dispensing probes for aspirating the sample and the reagent sense the liquid level with an aid of a liquid level sensing function, which is the technique described in Patent Document 1, for example, stop the immersion of the probe tip to a depth of a few or several millimeters in the sample or the reagent, and aspirate the sample or the reagent. The use of this sequence enables dispensing accuracy to be ensured by preventing an unnecessary amount of sample or reagent from being carried into or carried back from a reaction cell, and probe tip cleaning to be facilitated by ensuring an adequate sticking area of the sample or reagent on an outer wall of the probe.